1. Field of the Invention
The present invention relates to demountable connections for optical fibers, in particular demountable connections to hermetic optical fiber feedthrough.
2. Description of Related Art
Given the increasing bandwidth requirements for modern day data transmission (e.g., for high definition video data), fiber optic signal transmissions have become ubiquitous for communicating data. Optical signals are transmitted over optical fibers, through a network of optical fibers and associated connectors and switches. The optical fibers demonstrate a significantly higher bandwidth data transmission capacity and lower signal losses compared to copper wires for a given physical size/space.
In fiber optic signal transmission, conversions between optical signals and electrical signals take place beyond the terminating end of the optical fiber. Specifically, at the output end of an optical fiber, light from the optical fiber is detected by a transducing receiver and converted into an electrical signal for further data processing downstream (i.e., optical-to-electrical conversion). At the input end of the optical fiber, electrical signals are converted into light to be input into the optical fiber by a transducing transmitter (i.e., electrical-to-optical conversion).
The optoelectronic devices (receiver and transmitter and associated optical elements and electronic hardware) are contained in an optoelectronic module or package. The optical fiber is introduced from outside the housing of the optoelectronic module, through an opening provided in the housing wall. The end of the optical fiber is optically coupled to the optoelectronic devices held within the housing. A feedthrough element supports the portion of the optical fiber through the wall opening. For a variety of applications, it is desirable to hermetically seal the optoelectronic devices within the housing of the optoelectronic module, to protect the components from corrosive media, moisture and the like. Since the package of the optoelectronic module must be hermetically sealed as whole, the feedthrough element must be hermetically sealed, so that the electro-optic components within the optoelectronic module housing are reliably and continuously protected from the environment.
U.S. Patent Application Publication No. US2013/0294732A1 discloses a hermetic optical fiber feedthrough assembly in which the a hermetic ferrule assembly provides a demountable terminal for the optoelectronic package/module, for coupling to another optical device, such as an optical fiber ribbon (e.g., a patch cord having similarly shaped ferrules), using an alignment sleeve (e.g., a split sleeve having complementary shape sized to receive the ferrule assembly and the ferrule on the patch cord). The ferrule/terminal is low-profile, having a generally oval-shaped cross-section, supporting multiple optical fibers. The hermetic ferrule assembly may be deemed to be a demountable hermetic terminal of the package, that provides an alignment ferrule for optical alignment to external devices. With this embodiment, a defective external optical fiber ribbon may be replaced by plugging a replacement fiber ribbon onto the hermetical ferrule terminal, without having to replace the entire package, which can be quite expensive given the electronics contained in the package.
Current optical fiber connectors have not changed in basic design for many years. The basic connector unit is a connector assembly. The connector includes an assembly of components consisting of a ferrule, a ferrule housing, a cable jacket or boot, and other hardware provided within or outside the housing (e.g., cable strain relief, crimp, biasing spring, spacer, etc.). The ferrule and the terminating end faces of the fibers are polished. The ferrule in the optical fiber connector is spring-loaded to provide an axial preload bias to press together the polished end faces of the fibers in two connectors in an end-to-end configuration. In most cases, the intent is to establish physical contact between coupled fibers to prevent loss of light. Physical contact avoids a trapped layer of air between two fibers, which would increase connector insertion loss and reflection loss.
U.S. Pat. No. 5,261,019 discloses a demountable fiber optic connector includes a coil spring to bias the ferrule in the barrel of the connector against a connector end of a housing. As explained in this patent, in installation, an optical fiber connector experiences disruptive forces from time to time. For example, axial loads may be applied to a connector. The axial load may result from a person inadvertently pulling on a cable which is attached to a connector. If axial loads result in the connector ferrule moving away from an optically coupled opposing ferrule, the optical circuit may be disrupted or disconnected. Accordingly, fiber optic connectors should provide means for preventing disruption of the circuit in response to an axial load applied to the connector. The internal spring in the connector provides an axial preload on the connector ferrule, but also a twisting load (i.e., a torque loading) on the ferrule, which is undesirable as it could twist the ferrule (and hence the optical fiber held in the ferrule) to an extent affecting the optical alignment at the connection. Further, the connector disclosed in this patent is relatively bulky, given the various components including the coil spring in the connector. This connector works with relatively large connector structures, but would not be compatible with the relatively low profile, oval shaped ferrule connectors disclosed in PCT Patent Application Publication No. WO2014/011283A2 and U.S. Patent Publication No. US2013/0294732A1. The low profile ferrule connectors have small footprints, so they are particularly suited for connections of a high density of optical fibers (which are grouped into optical fiber cables) for a given space. Prior art connectors are too bulky, so less optical fibers/cables can fit into a smaller space.
What is needed is an improved approach to providing a preload to an optical fiber connector for a demountable connection to another connector or connector end of a housing, such as a hermetic optical fiber feedthrough assembly, which improves optical alignment, manufacturability, ease of use, functionality and reliability at reduced costs.